The BGS Lexicon of Named Rock Units — Result Details

Bryn Brith Member

Computer Code: BYN Preferred Map Code: BnB
Status Code: Full
Age range: Abereiddian Stage (O2) — Abereiddian Stage (O2)
Lithological Description: Massive lenticular beds of disturbed mafic tuff, tuffite and tuffaceous sandstone, with subordinate thin mudstones.
Definition of Lower Boundary: Conformable on the felsic ash-flow tuffs of the Offrwm Volcanic Formation or within the lowermost mudstones of the Cregennen Formation.
Definition of Upper Boundary: Conformable within the mudstones of the Cregennen Formation.
Thickness: To 65m, and might be locally up to 150m.
Geographical Limits: Cadair Idris district.
Parent Unit: Cregennen Formation (CREN)
Previous Name(s): Bryn Brith Beds [Obsolete Name and Code: Use BYN] (-3889)
Bryn Brith Grits (-742)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Crags of Bryn Brith. Pratt, W T, Woodhall, D G and Howells, M F. 1995. 
Reference(s):
Cox, A H, and Wells, A K. 1921. The Lower Palaeozoic rocks of the Arthog-Dolgellau district (Merionethshire). Quarterly Journal of the Geological Society, London, Vol.76, p. 254-324. 
Cox, A H, and Wells, A K. 1927. The geology of the Dolgelley district, Merionethshire. Proceedings of the Geologists' Association, Vol.38, 265-318. 
Pratt, W T, Woodhall, D G and Howells, M F. 1995. Geology of the country around Cadair Idris. Memoir of the British Geological Survey, Sheet 149. (England and Wales). (London: HMSO), 111pp 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E149